In open-end spinning machines, the sliver is fed into the spinning unit by a feed unit in which it is loosened by means of the functional lines of the fibre separating roller and thereby is transformed into a steam of loosened fibres which is fed by suction into the spinning rotor on whose collecting surface the fibres are collected into a fibre band and are then subjected to twisting by rotation and thus transformed into yarn, continually drawn away from the collecting surface, and wound on bobbin.
For the end-use properties of the yarn and for the spinning process stability it is very important to ensure that the fiber loosening out of the sliver is effected as perfectly as possible. The ideal state here is a uniform stream of seperated fibres. The more closely the spinning unit and its operational features come to this ideal state in the fibre separation, the better results can be achieved, especially in the production of high-grade fine yarns.
A detailed study of the fibre separation process, carried out with available technical means and accompanied by the respective measurements, has shown that the operational points of the fibre separating roller separate up to single fibres, only a part of to total fiber material, while the rest are only divided into groups consisting each of a varying number of fibres. The proportion between these two parts of fibers depends on the state in which the fibres are in the sliver and on other process parameters, especially on the number of fibres processed by the fibre separating roller in a time unit.
To deviations from the uniformity of the stream of separated fibres are, on the one hand, irregular and occuring at random in time, and, on the other hand, as established by repeated measurements, regular with a constant frequency corresponding to the frequency speed of the fibre separating roller; the latter effect is due to a sort of periodicity of the fibre separating roller which results from the fact that the functional lines are arranged on its surface along a helix line. In its most unusual version, which is the easiest to produce at the same time, the fibre separating roller is fitted with a saw-like coating wound in a helix groove, and varying in angles and dimensions so as to suit the particular fiber type to be processed.
Fibre separating rollers with saw-like coating arranged in a double-threaded helix line are also known, as well as those featuring needles inserted into their surface and acting as functional points. The various design versions of fiber separating needle rollers are aimed above all at a reduction of their production costs which are considerably higher than those of the saw-like coating type.
The known types of the fibre separating roller have their typical function properties as well as their drawbacks. The saw-like coating type ones are cheaper to produce and with various saw-like coatings can be sufficiently versatile.
A drawback of the saw-like coating type resides in that the helix arrangement pushes the fibres under separation, thus giving rise to irregularities in the stream of separated fibres. The multiple-threaded helix arrangement reduces the amplitude and increases the frequency of such deviations, at the same time still more intensely pushing the fibre fringe. The production costs of this version of the fibre separating roller are somewhat higher.
As a rule, the fibre separating needle rollers have a lower total number of functional points which affect the degree (i.e., the intensity) of the fibre separation. This is rather important in the production of relatively coarse yarns with a bulk of fibres passing through the spinning unit.